During the past decade, numerous instructional materials for teaching mathematics have been made available online, ready to be applied in classrooms. In this study, I focus on Open Educational Resources (OERs) that are shared on the GeoGebra Materials platform and created by their users. These dynamic materials are not supported by editorial teams who are following certain guidelines ensuring uniform styles and such resources have therefore inconsistent quality. For this reason, it is often difficult for teachers to quickly find “good” OERs to use in their own lessons which leads to my research aims. This study investigates quality criteria of dynamic materials for mathematics teaching and how their educational values can be described. Thi...